The rotor head of a helicopter typically includes means for articulating one or more blades through flapping, lag and pitch motions. To dampen the angular lag oscillations of the blades, resilient braces with viscoelastic, hydraulic or other damping means are used, typically referred to as lead/lag dampers. These are usually interposed between a peripheral edge of a rotor hub to which each blade is connected and the blade root.
One such damper incorporates a piston cylinder arrangement having hydraulic fluid disposed between a pair of chambers separated by an orifice. As the blade twists fore and aft (leads and lags) about a vertical hinge or axis, the fluid is driven to pass through the restrictive orifice at a controlled rate thus damping the lead/lag effect. However, such dampers are expensive to manufacture and lose damping ability if oil leakage occurs.
Another type of damper relies on a plurality of elastomer laminates which dissipate energy through shear deformation. Such a damper is shown in FIG. 1. The damper has a central shaft having a lug for attachment to a first structure such as a blade. A portion of the shaft has an elastomer laminate firmly bonded to it. A cylindrical housing envelops the elastomer laminate and extends axially with means for attachment to a second structure such as a rotor hub. For example, the central shaft may mount to the rotor hub and the housing may mount to the leading or trailing edge of the rotor blade. As the damper cycles in accordance with the lead lag oscillations, the elastomer laminate undergoes non-uniform shear strain, with the highest strain at the interface of the elastomer and shaft. Strains over 20% cause a temperature increase within the elastomer which may exceed 200.degree. F. The result is a significant loss of damping properties at the point of highest strain which can lead to erratic damping effectiveness and damper failure.